1. Field of the Invention
This invention relates to a clutch release apparatus for use in a motor vehicle, and in particular to a clutch release apparatus equipped with a diaphragm spring.
2. Description of the Related Art
A prior art clutch release apparatus is known from Japanese Utility Model Laid-Open Print No. 59-137422. This prior art shown in FIG. 11 discloses a clutch release apparatus equipped with a clutch release means for pressing a pressure plate 1 toward a clutch disc (not shown) by a plurality of coil springs 4 (only one is shown) each of which is between a clutch cover 5 and the pressure plate 1. A clutch facing 3 is provided between the pressure plate 1 and a flywheel 2 and the clutch facing 3 functions to transmit torque from the flywheel 2 to a shaft (not shown) fixed to the clutch facing 3. When the clutch release apparatus is not operated, the pressure plate 1 is pressed by each coil spring 4 to press the clutch facing 3 toward the flywheel 2 so that torque of the flywheel 2 is transmitted to the shaft to which the clutch facing 3 is fixed.
On the other hand, when the clutch release apparatus is operated, disengagement of the flywheel 2 from the clutch facing 3 is established due to the application of a force to the pressure plate 1 which overcomes the urging force of the plural springs 4 so as to prevent the transmission of torque from the flywheel 2 to the shaft to which the clutch facing 3 is attached.
However, in the foregoing clutch release apparatus, plural coil springs 4 have to be installed between the clutch cover 5 and the pressure plate 1 with the result that the axial length is increased and configuration of the clutch release apparatus becomes complex.
In light of the above-mentioned drawback, recently, a clutch release apparatus was proposed in which a diaphragm spring is employed instead of the conventional coil spring. This clutch release apparatus, as shown in FIG. 12, is equipped with a clutch cover 6, a diaphragm spring 7 supported by the clutch cover 6, a pressure plate 8 arranged in the clutch cover 6 and urged toward an output shaft (not shown) by the diaphragm spring 7. In this newly proposed clutch release apparatus, an outer peripheral portion 7a of the diaphragm spring 7 urges the pressure plate 8 toward the clutch disc by pressing against a fulcrum portion 8a of the pressure plate 8. The separation or disengagement of the pressure plate 8 from the clutch disc can be obtained by releasing the diaphragm 7 from its pressing engagement with the pressure plate 8. However, due to long-term use of the apparatus, the friction face of the pressure plate is subject to continual wear with the result that the point of contact between the diaphragm 7 and the pressure plate 8 is changed, thereby changing the clutch release characteristic. The foregoing is due to the shape of the support portion 8a being curved with a constant radial diameter R. Accordingly, the movement of the pressure plate 8 in the forward direction i.e., in the direction of the disc plate, increases the force required by a driver to depress a clutch pedal (not shown) and thereby release the clutch.